In the present study, dendritic cells showed slow movement at the beginning. The movement became more rapid after cultivation, with the cells eventually detaching from the culture vessel to swim freely in the medium. The detached cells exhibited various configurations through rapid appeaprance and disappearance of needle-like, fan-like, or other bizarre-shaped projections. Single cells moved forward and turned about in various directions. Aggregates of various numbers of cells were formed by attaching tails to each other or to some cell debris. In aggregates, each cell moved in its own direction, simulating a group of insects or birds flying in various directions at the same time. Death of cells usually occurred suddenly during active movements. This phenomenon reminds one of the story of a Greek who ran 26 miles and 385 yards to tell of the victory over the Persians, and then dropped dead. Mitotic figures of dendritic cells were observed, indicating that these cells are capable of proliferation in vitro.